For precisely positioning an image on a sheet of printing material, it is necessary to monitor, and if necessary or desirable, to correct the position of the image. The precise position of an image on the sheet of printing material may be important when, for example, the printed sheet is positioned on a feed path and being sent through a sheet-fed press that separately prints each color on the printed sheet; therefore, all colors must be precisely positioned to correctly print the image. While prior methods have been successful in identifying errors in the printing of images using a print making device, many prior methods perform error checking that is either expensive or use an offline or manual procedure. The offline procedures require the error checking to be completed after the image is printed, at which point only subsequent printing may be corrected.
For example, the published German Patent Document DE 44 01 900 C2, discloses a method for controlling the position of an image on a sheet in a sheet-fed printing press wherein the sheet is conveyed, printed, and monitored with respect to a deviation of the position of the image from sheet edges with regard to spacing and parallel position relative to a nominal or desired condition or phase. If necessary, suitable adjusting or positioning elements are manipulated, and the position of the image is thereby corrected. Performance of the method includes an image recording system arranged along the conveying path of the sheet, for obtaining image signals over the surface of the entire sheet. From the image signals, the spacing and the parallelism of the printing image to the paper edges of the sheet are derived, and deviations from nominal or set point values are determined. From the deviations, positioning signals for a corrective orientation of the image on the sheet are determined by the adjusting or positioning elements.
Since the entire surface of the sheet must be acquired by the image recording system in order to enable an evaluation of the position of the image on the sheet, the above method is expensive. Therefore, it would be advantageous to provide a less expensive method for correcting skew and lateral errors by identifying errors on the printed sheet and then adjusting the subsequent printed sheet and/or the print making device prior to printing.